1. Field of the Invention
The present invention relates to a charged particle beam exposure apparatus, and especially to the structure of an electrostatic deflection electrode; and to a method for manufacturing a charged particle beam exposure apparatus.
2. Related Arts
A charged particle beam exposure method using an electron beam or an ion beam is a known technique for exposing a fine pattern on the surface of a rectile during the forming of a semiconductor wafer or a mask. The charged particle beam exposure apparatus projects a charged particle beam, which is emitted by a charged particle beam gun, through a predetermined transmission mask, to form a beam whose cross section is a pattern to be exposed, and irradiates the surface of a sample with the beam. In this case, the beam must be deflected to a predetermined location of the sample surface.
For the deflection of the charged particle beam, there is employed a combination of an electromagnetic deflector, which sharply deflects a charged particle beam away from the center axis of the mirror barrel of an exposure apparatus, and an electrostatic deflector, which deflects a charged particle beam only slightly in a narrow region in the vicinity of the area in which deflection takes place. Although the electrostatic deflector, which is also called a sub-deflector, provides only a slight deflection effect, it uses only a comparatively low voltage for beam deflection, and it can increase the deflection speed. Conversely, although the electromagnetic deflector, which is also called a main deflector, provides a large deflection effect, deflecting a beam comparatively sharply, it requires a long setting time for beam deflection, and, as a result, it reduces deflection speed.
In the mirror barrel of an exposure apparatus, there must be provided, from the top, a charged particle beam gun, a primary transmsison mask, a secondary transmission mask, and the deflectors. In order to reduce the size of the mirror barrel, the electrostatic deflector and the electromagnetic deflector are overlapped in the portion wherein a projection lens is provided, immediately before the position for a sample is reached. Taking into consideration the relationship between a magnetic field and an electric field, the electrostatic deflector is located in a sealed cylinder in which is maintained a vacuum through which the charged particle beam passes, while the electromagnetic deflector and the projection lens (electromagnetic lens) are exposed to the external atmosphere.
The design for the electrostatic deflector calls for an arrangement of eight long cylindrical electrodes, for example, with a predetermined voltage being applied between each pair of facing electrodes. By applying a voltage to the four electrode pairs, it is possible to set as desired a deflection direction in a narrow sub-deflection region.
The present applicant proposed an electrostatic deflector described in U.S. Pat. No. 5,041,731 or in Japanese Unexamined Patent Publication Nos. Hei 2-247966 and 2-192117.
For an electrode of the electrostatic deflector, a ceramic is shaped into a cylinder and a groove is formed in the internal surface of the cylinder. The ceramic cylinder is then fired. After that, metal plating is performed to cover the entire internal surface of the cylinder formed of an insulating material, following which the plated layer in the groove is peeled away by an electric discharge. The electrodes are thus electrically separated to provide a plurality of pairs of electrodes. Unlike the metal electrodes, the thus produced electrostatic deflector electrodes has only plated metal layers on the surface of the ceramic. This can prevent an eddy current, which occurs due to changes in the magnetic field produced by the electromagnetic deflector located outside the electrostatic deflector.
However, the electrode structure for which metal plating is performed on the surface of the ceramic has the following problems.
First, since the procedure for the production of electrodes provides for extruded clay to be dried before it is fired, the shape of the clay electrodes has changed during being dried and by the time they are ready for firing. With eight electrodes, for example, the symmetry of their relationship will be lost, their sizes will differ, and their bodies will be twisted and deformed. Furthermore, during the firing process the same size changes occur. As a result of such size changes, beams are defocused and the aberrant deflection of beams occurs. In addition, the twisting of the bodies of the electrodes causes sub-deflection directions to be changed.
Second, it is known that since the electrostatic deflection electrodes are positioned the nearest to the sample, a resist made of an organic material coated on the surface of the sample is vaporized when irradiation with a beam is performed, and as a result a contaminant is deposited on the surfaces of the electrodes. Also, scattered electrons that are generated by the irradiation of charged particles may strike organic material in the vacuum and cause contaminants to be attached to the surfaces of the electrodes. Such contamination of the electrodes causes a charge-up on the electrode surfaces; it also results in the deterioration of the accuracy with which beams are deflected and in the defocusing of beams.
In order to eliminate the contamination, the present inventors proposed a method for cleaning the surfaces of components in an exposure apparatus by performing plasma excitation of oxygen that is introduced into the apparatus (e.g., Japanese Patent Application No. Hei 5-138755). With this cleaning method, however, since the application of a high frequency to a mirror barrel accompanies the generation of plasma, the plating on electrode surfaces is scored by the sputtering of generated ions, and when the cleaning is repeated a number of times, the plated metal layers will be peeled away and the ceramic will be exposed. Thereafter, a charge buildup will occur relative to the exposed ceramic. It was confirmed by the present inventors that even with a plated layer of 1.5 .mu.m, a charge buildup occurred when cleaning using oxygen was performed more than ten but less than twenty times. As a result, the life expectancy of electrodes is shortened and the ratio relative to the operation of the exposure apparatus is reduced.
Although the problem concerning plated layers can be resolved by forming electrodes of metal, as was previously described, metal electrodes will cause an eddy current due to changes in the magnetic field produced by an electromagnetic deflector. With the occurrence of an eddy current, the time constant for the setting time becomes several msec, and in consonance with this, there is a deterioration in the exposure throughput.